1. Field of the Invention
The invention relates generally to structures for latching a lid to a pressure vessel and for preventing release of the latching mechanism while certain pressure conditions exist within the vessel. In particular, the invention relates to a manually operable latching mechanism and safety lock useful for opening and closing of the lid of a pressure fryer.
2. Description of the Prior Art
Pressure vessels have long been known to be useful in a wide variety of situations, such vessels invariably including a lid which allows access to the interior of the pressure vessel. Such lids must be sealed on closure of the vessel and positively latched by a mechanism which preferably allows ready opening and closure of the lid with a minimum of effort but with a maximum of safety. A common environment in which pressure vessels are used relates to the cooking of foods under pressure, such devices typically being referred to as pressure cookers or pressure fryers. In this use environment, foods are typically cooked in oil and, under the cooking conditions, moisture in the food is released into the oil as an unavoidable result of the cooking operation, the moisture being prevented from expansion even at the relatively high cooking temperatures by the internal pressure of the cooker. Care must be taken in the design of a pressure cooker to prevent inadvertent and abrupt removal of the pressure cooker lid during and immediately after the cooking operation when the temperature and pressure within the cooker is high. Such an inadvertent opening of the pressure cooker allows immediate expansion of the moisture entrapped in the oil due to the vapor pressure of the moisture, the result being an explosion of the hot oil through the opening normally secured by the lid. An inadvertent and untimely opening of a pressure cooker lid in this manner represents a substantial hazard to an operator of the cooker.
While it is important that the lid of a pressure cooker be secured in a positive manner to prevent accidents, the mechanism employed for securing a lid to a pressure cooker must be capable of ready and rapid operation in both the closing and opening of the lid so that the cooker can be efficiently utilized in commercial cooking operations. While the hazards associated with pressure cookers are recognized and are taken into consideration in the design of latching mechanisms for pressure cooker lids, it is necessary to provide a latching mechanism which is operable by a single individual in a rapid fashion although with due attention to the task, particularly since in a commercial situation the operator is usually also engaged in other tasks in addition to operation of one or more pressure cookers. A particular advantage to an operator of one or more pressure cookers would be the ability to open and close the lid of the cooker with minimum effort consonant with due attention to safety, thereby allowing attention to be also given by the operator to other tasks which are typically associated with cooking of foods in a commercial operation where efficient use of time is absolutely required. In such situations as are commonly encountered in "fast food" cooking operations, it is necessary for an operator of a pressure cooker to read pressure gauges or otherwise make decisions relative to a proper time for opening of a pressure cooker on completion of the cooking cycle. In such situations, it is necessary to provide a locking mechanism which is an added check to the operator's decision to prevent opening of the pressure cooker lid until such time as pressure conditions within the cooker allow safe opening of the cooker. Such a locking mechanism must be reliable and relatively incapable of being fouled and thus rendered inoperable even under the conditions encountered in a commercial cooking operation.
Commercial pressure cookers which are commonly employed are of the type disclosed by Wagner in U.S. Pat. Nos. 3,159,095 and 3,314,416, these pressure cookers being primarily utilized to fry chicken and similar foods which are cooked on the premises by relatively untrained personnel. The pressure fryers disclosed by Wagner include lids which are sealed against a fryer pot opening by means of a pivoted bar which extends over the lid and contacts the lid centrally thereof, a manually operable spindle screw extending through the bar medially of its length and engaging the lid in the vicinity of the contact area between the lid and the bar. These prior art and widely used commercial cooking units also employ a hand-operated lift mechanism disposed at the distal end of the bar for engaging a lug or latch formed in the body of the cooking pot. Accordingly, one operation is required to release the bar from sealing engagement with the lid by means of a screw spindle and a second operation is required to operate the lid to disengage said lift from the catch. The full attention of an operator along with the use of both hands is thus required to operate the essentially separate sealing and latching mechanisms of the pressure fryers disclosed by Wagner. Further, the operator of the Wagner fryers has reliance only on attention to a pressure gauge mounted on the fryer in order to determine when the sealing and latching mechanisms can be operated after completion of the cooking cycle since no locking mechanism is employed to prevent opening of the fryer prior to a sufficient reduction in pressure within the fryer to render safe the opening of the fryer.
Stoermer, in U.S. Pat. No. 3,976,218 improves the pressure fryers of the Wagner patents by provision of a safety interlock which prevents operation of a screw spindle and maintains a closure bar in sealing engagement with the lid of a pressure fryer. The Stoermer safety lock comprises a vertically extending pin which is biased upwardly into an effective engagement with the screw spindle by pressure within the fryer acting against a lid liner, the liner biasing the pin upwardly to prevent rotation of the screw spindle. Since the channel within which the pin is held is vertically disposed with the upper end thereof being essentially open to ambient, fouling of the locking mechanism due to dripping of congealable liquids as well as dropping of solid matter such as breading and the like associated with a cooking operation provides the potential for inadequate operation of the locking structure. Failure of such a safety interlock to operate is hazardous even though the operator of the pressure cooker must primarily rely upon his own personal judgement as to the safety of proceeding with the opening of the pressure cooker.
The present invention intends improvement over the prior art for pressure vessels generally and pressure cookers and fryers particularly in that a latching mechanism is provided which allows ready and rapid opening and closure of the lid of a pressure vessel, the opening and closure operations being readily carried out by a single individual with the use, if desired, of only one hand and essentially with one motion. Further, the invention provides a locking mechanism operable with the latching mechanism to positively prevent opening of a pressure vessel lid while dangerous pressure conditions exist within the vessel. According to the present invention, the locking mechanism is configured to inhibit fouling of the mechanism by congealable liquids and solids such as breading and the like, thereby rendering operation of a pressure vessel such as a pressure cooker or fryer to be safe to a degree not heretofore realized in the art.